The present invention relates generally to fuel systems and more particularly to controlling vapor generation in fuel systems.
Known types of on-board fuel vapor management systems comprise a vapor collection canister that collects and stores fuel vapor emitted from a tank containing volatile liquid fuel for the engine. A canister purge solenoid (CPS) valve periodically purges collected vapor to an intake manifold of the engine where it entrains with induction air or with an induction air-fuel charge for combustion in the engine combustion chamber space. One type of CPS valve comprises a solenoid that is under the control of a microprocessor-based engine management system. Because vapor storage systems such as carbon canisters have a finite capacity to adsorb fuel vapor, fuel vapor may be periodically emitted into the atmosphere when vapor storage systems exceed adsorption capacity.
Other solutions have been proposed to reduce the tendency of fuel to vaporize. One way is by an enclosure, such as a bladder or diaphragm for example, arranged within a fuel tank to reduce the volume of vapor headspace in the tank. Another proposed solution is to pressurize the headspace to a superatmospheric pressure to reduce the volatility of the fuel. Yet another proposed solution, as described in U.S. Pat. No. 5,868,120 (the ""120 patent), combines these two principles. In the ""120 patent, a flexible bladder is placed within the fuel tank to reduce the volume of tank headspace that can be occupied by fuel vapor. A source of pressurized gas introduces gases within the bladder and within the headspace through a solenoid operated bladder pressure valve to pressurize the tank to superatmospheric pressure. In addition, a series of valves are available to vent the gas as needed. An engine control module controls the selective pressurizing and venting in accordance with various inputs.
In the ""120 patent, however, vapor generation is attenuated, not eliminated. As such, in conditions where the pressure buildup within the headspace is high (above 27 inches of water as detected by sensor 98 in a preferred embodiment), a vent valve is opened to vent the air/fuel vapor mixture to a carbon canister, wherein the fuel vapor is stored. If the amount of fuel vapor in the canister exceeds the adsorption ability of the activated carbon pellets or other adsorbing material within the canister, fuel vapor may be vented into the atmosphere. Further, a purge system must be added to periodically purge the canister of fuel vapor.
Thus, it is highly desirable to create a fuel system that eliminates vapor generation during running modes and diurnal cycles (engine off mode) in the fuel tank. This would have the added benefit of eliminating the need a carbon canister and purge system.
The objects of the present invention are achieved by introducing a flexible, low-permeation conductive fuel bladder contained within a low or medium pressure vessel (or fuel tank) to hold liquid fuel. Air pressure, supplied by an air pump or comparable device, introduces air pressure to the outside of the bladder to keep the bladder against the fuel and to prevent vapor generation during running modes and diurnal cycles. Valves located within the tank may release pressure as needed. Sensors located within the system send information to an electronic control module regarding fuel level, tank pressure, battery voltage, air temperature, fuel pump speed, fuel filler door state, and fuel temperature. The electronic control module interprets these signals and instructs the system to selectively increase, decrease, or hold steady the pressure within the fuel system to maintain the bladder against the fuel based on the information received. A fuel delivery pump, external to the tank, pressurizes the fuel to a desired pressure to be used by an engine.
The present invention eliminates the need for a carbon canister or purge system to remove fuel vapor from the fuel system because the disclosed system works to eliminate fuel vapor generation during running modes and diurnal cycles. Further, the bladder system improves the safety features in a storage tank by adding a second barrier to the environment and improves safety by eliminating potentially harmful fuel vapor generation.
During refueling operations, the fuel cap is removed and the bladder system is returned to atmospheric pressure. The fuel nozzle is inserted through a mechanical seal in the refueling pipe. This minimizes refueling losses and prevents air from entering the system. When the refueling is accomplished, the system is repressurized if conditions require it by an electric or mechanical air pump to prevent vapor generation.
Further, in automotive applications, fuel vapor generation is minimized even when the engine is turned off, as the system is sealed and will remain pressurized to keep the bladder against the surface of the fuel.
The present invention adds little complexity to a fuel system and can be easily integrated into conventional fueling infrastructures.
While the present invention is ideally suited for use in automotive fuel tank systems, it is contemplated that this system may be used in a wide variety of settings where vapor generation can occur. This may include underground fuel storage tanks, stationary power sources, and portable power sources.
Other objects and advantages of the present invention will become apparent upon considering the following detailed description and appended claims, and upon reference to the accompanying drawings.